Efficient Hydrogen Generation Research Articles

Heterostructured FeP4/CoP@NF as trifunctional electrocatalysts for energy-efficient hydrogen production

The developing of efficient and cost-effective electrocatalysts for hydrogen evolution is of great significance to the development of hydrogen energy. It is believed that the efficient hydrogen generation of water cracking is restricted from the slow oxygen evolution reaction (OER) process. Consequently, it is highly recommended to find alternative anodizing to produce hydrogen to reduce electricity consumption. Urea oxidation reaction (UOR) is an alternative to the traditional anodic OER. In this paper, an electrocatalyst FeP4/CoP@NF-7.5 supported on nickel foam (NF) was designed by using a template-directed growth and low-temperature phosphating method. The FeP4/CoP@NF-7.5 with a rich interface gives it more active sites and enhances mass transfer and conductivity, possessing excellent catalytic performance against hydrogen evolution reaction (HER), OER and UOR in alkaline electrolyte. Thanks to the abundant interface and bimetallic synergy, the designed catalyst exhibits the overpotentials of 45 mV and 259 mV for HER and OER to transfer 10 mA cm−2. In addition, FeP4/CoP@NF-7.5 also possesses significant catalytic activity against UOR of 136 mV (j10) in 1 M KOH with 0.33 M urea, which provides another alternative to the low efficiency of OER through the reduction of hydrogen production costs. Finally, the overall water splitting test was undertaken in 1 M KOH containing/free of 0.33 M urea. Remarkably, only 1.43 V is required to drive on urea electrolyzer (j10 = 10 mA cm−2), while 1.52 V are gained on water electrolyzer. This paper lays the foundation for the developing of high-active transition bimetallic phosphide electrocatalysts for energy-saving hydrogen production.

Efficient photocatalytic hydrogen evolution via interfacial engineering and charge carrier utilization with WSP/g-C3N4 S-scheme heterojunction

The practical implementation of photocatalytic hydrogen generation faces challenges due to the rapid recombination of photogenerated electron-hole pairs. This study reports the synthesis of a WSP/g- C3N4 S-scheme heterojunction catalyst featuring exposed hydrogen evolution active W sites, achieved through in-situ P introducing. Remarkably, the WSP/g-C3N4 catalyst exhibits a superior photocatalytic hydrogen evolution rate of 3.92 mmol h−1 g−1, surpassing g-C3N4 and attaining 112 times the performance of pristine C3N4. A series of characterization techniques and Density functional theory (DFT) reveal that WSP/C3N4 possesses the following advantages as a photocatalyst: 1) Under visible light irradiation, the distinctively ordered and well-crystallized structure generates potential differences, facilitates charge transfers, and enhances the hydrogen evolution activity. 2) The coupling between WSP and g-C3N4 interfaces effectively promotes the directional migration of photogenerated electrons. 3) The shallow bound energy level introduced near the conduction band of WSP effectively prolongs the carrier lifetime. These features collectively contribute to the improved performance of photocatalytic hydrogen evolution. These features collectively contribute to the improved performance of photocatalytic hydrogen evolution. This finding suggests new ways to create organic/inorganic heterojunction composite photocatalysts for efficient hydrogen generation.

A flexible load adaptive control strategy for efficient photovoltaic hydrogen generation system

The adaptive adjustment of the input current in proton exchange membrane electrolyzers (PEMEL) can provide several benefits, including the enhancement of PEMEL efficiency and the extension of its operating lifespan within an optimal range. This study presents a novel configuration for a photovoltaic (PV) hydrogen generation system that allows for the direct integration of PV. Moreover, the utilization of the triple-phase shift (TPS) modulation technique is implemented in order to achieve maximum power point tracking (MPPT) control within dual active bridge (DAB) DC/DC converters. The proposed strategy offers a pre-control approach for active adjustment of flexible loads to mitigate the mismatch between power output and load caused by fluctuations in renewable energy sources. This mismatch can lead to excessive current ripple, which in turn can impact the safe functioning of the PEMEL. In tandem with the analysis of the factors that contribute to ripple and the properties of the Electrical Spring (ES), relevant multiple variables are selected as control signals for the control strategy. This is done to effectively regulate the magnitude of non-essential loads and consequently reduce the ripple in the PEMEL system. The use of the ES pre-control technique effectively addresses the issue of delayed response of the PEMEL to PV oscillations, which is attributed to the large time-lag characteristics of electrolyzers. The simulation results at steady-state conditions and sudden changes in lighting conditions demonstrate concurrently that the overall control strategy yields a reduction in current stress in the DAB to 30.09% and 51.59%, respectively, enables MPPT in PV systems, and decreases the input current ripple of PEMEL to 80.1% and 57.67%, showing stronger anti-disturbance ability.

Energy, efficiency, and environmental analysis of hydrogen generation via plasma co-gasification of biomass and plastics based on parameter simulation using Aspen plus

Energy, efficiency, and environmental analysis of hydrogen generation via plasma co-gasification of biomass and plastics based on parameter simulation using Aspen plus

Architecture of urchin-like TiO2 integrated ultrasmall Rh nanoparticles with oxygen vacancy-reinforced electronic metal-support interaction for boosting hydrogen production from ammonia borane hydrolysis

Metal oxide-supported Rh nanoparticles (NPs) can provide abundant catalytically active sites for hydrogen evolution from ammonia borane hydrolysis (ABH). Considering the scarcity and high cost, developing effective strategies to reduce the utilization of Rh and simultaneously improving its catalytic activity is absolutely needed. Here, we develop ultrafine Rh NPs anchored on oxygen vacancies (VO)-bearing urchin-like TiO2 (U-TiO2). VO can facilitate the formation of electron-rich metallic Rh surface and boost the H2O dissociation, leading to highly efficient hydrogen generation from ABH without alkali promoters. Noticeably, the temperature-controlled annealing of the Rh/U-TiO2 precursor at 450 °C in reducing atmosphere generates the maximum VO concentration. This arouses strong electronic metal-support interaction between the Vo and Rh NPs to yield electron-rich metallic Rh surface. The obtained Rh/UT-450Vo exhibits a high initial turnover frequency of 1729 min−1 for ABH without alkali promoters, outperforming that of the contrast samples and most of previously developed Rh catalysts. This finding offers an effective strategy to fabricate high-efficiency metal oxide-supported metal NPs toward catalytic hydrogen production.

3D printing Al porous metamaterials with triply periodic minimal surfaces (TPMS) for hydrogen generation from Al-water reaction

Porous metamaterials with three-dimensional periodic minimal surfaces provide new inspirations to develop catalytic hydrogen generation materials owing to their excellent mass transfer. Herein, ten kinds of Al porous metamaterials with triply periodic minimal surfaces (TPMS) were prepared by selective laser melting (SLM) for hydrogen generation from Al–H2O reaction. The structures of TPMS type Al materials significantly affect their hydrogen generation performance, and the increased reaction area and liquid flow rate of TPMS structure can effectively improve the galvanical replacement reaction and rapidly form a Ni/Al battery, thus accelerating the hydrogen generation. Compared to conventional aluminum powder, the obtained Diamond type Al porous metamaterial exhibit short induction period, high hydrogen generation yield (81.4 % after 2 h reaction) and high hydrogen generation rate (468 mL-H2·min−1·gAl−1), easy activation of surface passivation film, good structural stability and convenience to recycle the materials after use. This work highlights a simple, low-cost and optional porous structure design strategy that can be applied in the field of safe and efficient catalytic hydrogen generation.

Highly Efficient Nitrogen-Fixing Microbial Hydrogel Device for Sustainable Solar Hydrogen Production.

Conversion of sunlight and organic carbon substrates to sustainable energy sources through microbial metabolism has great potential for the renewable energy industry. Despite recent progress in microbial photosynthesis, the development of microbial platforms that warrant efficient and scalable fuel production remains in its infancy. Efficient transfer and retrieval of gaseous reactants and products to and from microbes are particular hurdles. Here, inspired by water lily leaves floating on water, a microbial device designed to operate at the air-water interface and facilitate concomitant supply of gaseous reactants, smooth capture of gaseous products, and efficient sunlight delivery is presented. The floatable device carrying Rhodopseudomonas parapalustris, of which nitrogen fixation activity is first determined through this study, exhibits a hydrogen production rate of 104mmolh-1 m-2 , which is 53 times higher than that of a conventional device placed at a depth of 2cm in the medium. Furthermore, a scaled-up device with an area of 144 cm2 generates hydrogen at a high rate of 1.52 Lh-1 m-2 . Efficient nitrogen fixation and hydrogen generation, low fabrication cost, and mechanical durability corroborate the potential of the floatable microbial device toward practical and sustainable solar energy conversion.

Decoration of spherical Sb2S3 over CuO nanoflakes for efficient photoelectrochemical hydrogen generation

Developing an efficient photocathode system from earth abundant materials is essential for effectual Photoelectrochemical (PEC) water splitting. Charge transfer between heterojunctions is important in fabricating a novel photocathode, keeping cost-effectiveness, abundance, and PEC performance in mind. The p-type narrow band gap photocathode, CuO (Eg = 1.5 eV) synthesized by hydrothermal method, was decorated with Sb2S3 Nanospheres (NSs) by adopting a facile chemical bath deposition (CBD) procedure to fabricate CuO/Sb2S3 NSs heterojunction. Fabricated heterojunction showed better PEC performance contrary to bare CuO, improvement in photocurrent density CuO/Sb2S3 NSs (J = −1 mA cm−2) than CuO (J = −0.3 mA cm−2) photoelectrode at 0 VRHE in 0.5 M Na2SO4 (pH 6.85) is due to enhanced charge carrier generation/separation. The photostability of CuO/Sb2S3 remains intact for 2.5 h with no degradation in photocurrent density. Sb2S3 works as a sensitizer, diminishing the recombination rate of the e−/h+ in CuO/Sb2S3 NSs. UV–Visible and photoluminescence(PL) emission spectra results suggested CuO/Sb2S3 enhanced absorption spectrum and reduced rate of recombination. Electrochemical impedance spectroscopy studies show less charge transfer resistance for CuO/Sb2S3 NSs than CuO. This finding will pave new path in developing novel photocathodic material configurations and heterojunction with Cu-based binary oxides/chalcogenides for solar harvesting.

Non-Precious Metals Catalysts for Hydrogen Generation

In this paper, the generation of hydrogen from alkaline sodium borohydride solution by hydrolysis is studied. To obtain catalysts for efficient hydrogen generation, Ni, Mn, Mo, and Co metals were deposited on the Cu surface by the simple electroless metal deposition method using morpholine borane as a reducing agent. Depending on the peculiarities of the deposition of each metal, the coating thickness was ca. 1 μm for all catalysts. The deposited coatings were compact and crack-free, with multilayer characteristics and a cauliflower-like structure. The prepared Ni/Cu, NiMn/Cu, NiMo/Cu, NiCo/Cu, NiCoMn/Cu, NiCoMo/Cu, and NiCoMoMn/Cu catalysts showed an efficient catalytic activity for sodium borohydride hydrolysis reaction. The lowest activation energy of 45.3 kJ mol−1 for sodium borohydride hydrolysis reaction was obtained using the NiCoMoMn/Cu catalyst. The highest hydrogen generation rate of 3.08 mL min−1 was also achieved using this catalyst at 303 K. With a further increase in temperature to 343 K, the hydrogen generation rate catalyzed by the NiCoMoMn/Cu increased 7.7 times and reached 23.57 mL min−1.

Nickel and/or platinum modified crystalline silicon–carbon composites and their electrochemical behaviour towards the hydrogen evolution reaction

Generation of hydrogen is very important, as it is one of the most desired alternatives to fossil fuels. Moreover, designing of cheap and stable electrocatalysts is the task for the efficient generation of hydrogen with reasonable activity. Materials hybridization can be considered a tool for engineering different material properties. Composites of modified silicon such as C–Si, Ni/(C–Si), Pt/(C–Si), and Pt–Ni/(C–Si) were prepared (in weight percent) and studied as electrocatalysts for the hydrogen evolution reaction (HER) in 0.5 M H2SO4 solution. The surface morphologies and chemical compositions of the composites were confirmed using transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDX), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), X-ray fluorescence analysis (XRF), elemental mapping, and BET surface analysis. The electrochemical measurements of linear sweep voltammetry (LSV), Tafel plots, chronoamperometry, and electrochemical impedance spectroscopy (EIS) were used to study the behaviour of the prepared electrodes toward the hydrogen evolution process. Among the various prepared composites, [7%Pt–3%Ni]/[C–Si (1:1)] composite shows the best catalytic activity with the highest HER rate (940.95 µA cm−2 s−1), the lowest overpotential [0.358 V vs. (Ag/AgCl) ≈ 0.161 V vs. (RHE)] at 10 mA cm−2, and the lowest charge transfer resistance (2.657 Ω) compared to other prepared electrodes. In addition, it gives the highest values of 4.219 × 10−3 s−1 turn over frequency (TOF) and 642 mA g−1 mass activity. It shows good stability towards the hydrogen evolution reaction as the current density reaches about 34.28 mA cm−2 after 5 h.Graphical abstract

Surface Modification of Nickel Titanate Nanocubes with Ultra‐small Palladium and Platinum Nanocrystals to Promote Solar Hydrogen Generation under Visible Light

AbstractModification of nickel titanate nanocubes with metal nanocrystals is a viable approach to build a Schottky heterojunction for efficient hydrogen generation. The deconvoluted XPS spectrum of Pt 4 f (peaks at 72.0 and 75.5 eV corresponding to Pt° and Pt2+) and Pd 3d3/2 (335.4 and 336.7 eV corresponding to Pd° and Pd2+) and presence of lattice fringes in HRTEM at 2.19 Å of Pd°, reveal the formation of heterojunction in Pd−NiTiO3 and Pt−NiTiO3 nanocubes. The solar hydrogen generation investigation exhibits 2‐fold enhancement in HER (130 and 165 μmol g−1 h−1 while using Pt−NiTiO3 and Pd−NiTiO3, respectively) than that of bare NiTiO3 (88 μmol g−1 h−1). The creation of heterojunctions between titanates and metal nanoparticles, facilitating efficient transport of photo‐generated electron to empty or partially filled d or f orbitals of metals, thereby lowering electron‐hole recombination rate, as revealed by shorter average lifetime 29 ns (Pd−NiTiO3) than 64 ns (NiTiO3). Further, the unison of faster charge transfer kinetics as revealed by the Nyquist plot, more negative flatband potential (Efb −0.3 vs. RHE) leading to appropriate band bending, reduced overpotential requirement, higher oxygen vacancies (19.46 %) and uniform dispersion of metal atoms on NiTiO3 surfaces that are acting as trapping centers etc. are enabling improved hydrogen generation in the case of Pd−NiTiO3.

Development of Cobalt Oxide-Decorated Reduced Graphene Oxide-Supported Nickel Alloy Coating for Efficient Photocatalytic Hydrogen Generation

Development of Cobalt Oxide-Decorated Reduced Graphene Oxide-Supported Nickel Alloy Coating for Efficient Photocatalytic Hydrogen Generation

Triazine- and porphyrin-based donor-acceptor microporous conjugated polymers for enhanced photocatalytic hydrogen production activity

Donor-acceptor type conjugated microporous polymers (D-A CMPs) have recently gained popularity as active components for photocatalytic hydrogen evolution from water due to their ability to separate the photoinduced holes and electrons efficiently and vastly absorb visible light. However, creating a novel CMP photocatalyst with high photoconversion efficiency is still difficult. Porphyrins and triazines exhibit intriguing electrical and optical features. We present here the directed synthesis and photocatalytic activity in hydrogen generation of two donor-acceptor isostructural triazine- and porphyrin-based conjugated microporous polymers (H-Por-TPT and Zn-Por-TPT CMPs). Our data demonstrate that both CMPs have extremely high specific surface areas (around 650 m2 g−1) and thermal stabilities (Td10: equal to 629 °C with char yields equal to 76.18 wt%). Introducing a Zn atom into a porphyrin ring profoundly influences its optoelectronic properties and photocatalytic efficiency for hydrogen generation from water. Zn-Por-TPT CMP has one of the highest reported values for a D-A CMP, with a photocatalytic hydrogen evolution rate of 11450 μmol g−1 h−1 when exposed to visible light. In addition, the Zn-Por-TPT CMP is notable not just for increasing the rate of hydrogen generation but also for improving photocatalysis stability during prolonged irradiation for roughly 30 h. These CMPs may prove useful as organic photocatalysts in future photocatalytic H2 production from water applications.

Phosphorus coordinated Co/Se2 heterointerface nanowires: in-situ catalyst reconstruction toward efficient overall water splitting in alkaline and seawater media

Designing a highly efficient electrocatalyst to realize overall water splitting is vital, yet identifying the active site remains an ongoing challenge. Herein, the electrochemical in situ surface activation of P@Co/Se2-NW/CC was investigated to understand the enhanced OER activity of P@Co/Se2-NW/CC. The incorporation of phosphorus is thought to increase the vacancies surrounding the Co cations in the initial Co/Se2 and speed up the structural change into "active species" like cobalt oxide/oxyhydroxide. The as-synthesized P@Co/Se2-NW/CC required a low overpotential for OER (η100 = 230 and 280 mV) and HER (η100 = 111 and 132 mV), respectively, in alkaline water and alkaline seawater media. In-situ infrared reflection-absorption spectroscopy (IRRAS) and Post characterization unraveled the existence of surface-bounded Co oxide species on P@Co/Se2-NW/CC after OER catalysis, which is responsible for the enhanced electrocatalytic activity. This study offers a valuable strategy for developing noble-metal-free bifunctional catalysts for efficient hydrogen generation from alkaline seawater and alkaline water electrolysis.

Microwave-intensified hydrolysis for high efficiency hydrogen generation over magnetically separable Co3O4-carbon nanotube composites

Microwave (MW)-assisted process intensification technology has the potential to improve catalytic conversion under mild reaction conditions. In this study, a series of MW-sensitive CNTs-Co3O4 composites were designed and synthesized as catalysts for the conversion of NaBH4 to H2. It was found that MW irradiation leads to a 19.6 (35 °C) to 49.5% (55 °C) increase in the hydrogen generation rate (HGR) of NaBH4 hydrolysis catalyzed by the CC14, which is attributed to the combined contribution of thermal and non-thermal effects of microwave irradiation. Moreover, the NaBH4 hydrolysis catalyzed by CC14 catalyst at different heating modes followed the zero-order kinetic model, and the pre-exponential factor of NaBH4 hydrolysis catalyzed by CC14 catalyst under MW irradiation was approximately 157 times higher than under conventional heating, indicating that microwave irradiation increased the effective collision frequency at the reaction interface of CC14 catalyst. In addition, the selective and instantaneous heating of microwave irradiation was demonstrated by using a specially designed pseudo-homogeneous low temperature reaction system. Moreover, DFT calculations show that the rate-determining step of NaBH4 hydrolysis is H2O dissociation.

Hydrogen production of flat plate solar collectors integrated with photovoltaic thermal panels

This study investigates an integrated system's energetic and exergetic evaluations and hydrogen generation efficiency. The proposed system comprises flat plate solar collectors (FPSCs) and photovoltaic thermal panels (PV-Ts) having a total area of 112.32 m2 and 108 m2, an organic Rankine cycle (ORC) containing n-butane as working fluid, a proton exchange membrane (PEM) electrolyzer, a building for fungus production and a storage tank for hot water demand a house. The system analyses are conducted by Engineering Equation Solver (EES) software for a daily solar radiance in July. While the PV-T is refrigerated by the water in the city network with a heat exchanger, warm water is obtained from the PV-T as well as increasing the electricity generation of the PV-T. Thus, a thermal gain is provided by sending the preheated water from PV-Ts to FPSCs. Consequently, when both collectors worked together, fluid was obtained at a minimum and maximum temperature of 100 °C and 132.3 °C during the day. Thus, thanks to both collectors, a higher temperature fluid was sent to the ORC. In addition to the electricity generated by the PV-Ts in the system, electricity is also generated by the ORC from pre-heated hot water by two collectors. Thus, ORC produced a total of 173.96 MJ of electricity during the day, while PV-Ts produced a total of 341.04 MJ throughout the day. Thus, the entire system produced a total of 515 MJ of electricity throughout the day. The total generated electricity is operated in the PEM electrolysis for generating hydrogen via the water electrolysis process in the system. Only the electricity generated by ORC produces 784.18 g of hydrogen per day, while only the electricity generated by PV-Ts produces 1618.4 g of hydrogen. Thus, a total of 2402.58 g of hydrogen is generated by the system. The overall energetic performance of PEM was varied between 67.16% and 69% during the day. The maximum energetic and exergetic performance of the system is 37.02% and 7.32%, while the minimum energetic and exergetic performance is 31.70% and 6.88%, respectively.

ZnS-stabilized single atoms for highly-efficient water electrolysis

Efficient generation of hydrogen via water electrolysis provides a strategy for producing clean and sustainable fuel. Nevertheless, the sluggish cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER) require much energy input to overcome the high overpotential. Rational design of electrocatalysts is of crucial importance for enhancing the HER and OER performance. Herein, metal single atoms stabilized on the ZnS support (M@ZnS) were systematically investigated as the electrocatalysts for HER and OER via the density functional theory (DFT) calculations. Volcano plots were established to screen HER and OER catalysts with excellent performance. The structural, thermodynamic and electrochemical stability of M@ZnS catalysts were investigated. Sn@ZnS and Ni@ZnS exhibit superior HER catalytic activity. In particular, the ΔGH∗ value of Sn@ZnS is 0.049 eV, which is lower than that of the well-known benchmark Pt catalyst. Sn@ZnS and Pt@ZnS show good OER activity, thus they are expected to be the promising OER electrocatalyst candidates. The overpotential values of Sn@ZnS and Pt@ZnS are 0.60 V and 0.42 V, respectively. Sn@ZnS can work as a bifunctional HER/OER electrocatalyst for water electrolysis. This work not only provides theoretical guidance on the design of low-cost electrocatalysts toward HER and OER, but also paves a new way to stabilize single atoms for the fabrication of single-atom catalysts.

Size-Controlled Synthesis of IrO2 nanoparticles at High Temperatures for the Oxygen Evolution Reaction

Polymer electrolyte membrane (PEM) electrolysis is considered to play a vital role in the sustainable energy transition. The efficient generation of hydrogen is largely influenced by the slow rate of the anodic oxygen evolution reaction (OER). Iridium oxide represents one of the most promising catalysts for the electrochemical oxidation of water in an acidic environment. Under harsh operating conditions at the anode, iridium oxide is found to be among the most dissolution-resistant catalysts while offering acceptable OER activity. However, iridium’s limited availability dictates high costs centralizing the research in direction of reducing noble metal content while maintaining favorable electrochemical properties.[1] Designing nanostructured catalyst with an increased surface-to-volume ratio improves the application-oriented mass-specific activity.[2] Hydrous iridium oxide is known for superior OER activity, but for a successful application, drastic dissolution of the catalyst must be addressed by stabilization. This can be achieved by heat treatment to temperatures ≥400ºC with the formation of crystalline order. However, managing to avoid agglomeration of nanoparticles at high temperatures is not trivial, thus, temperature studies on electrochemical stability and activity on similar particle sizes are missing.[3]. Here, we demonstrate how nanoparticles below 10 nm can be obtained at high preparation temperatures up to 800 °C with unprecedented control over particle size and morphology. A detailed understanding of the structural evolution during heating was obtained by in-situ scanning transmission electron microscopy (in-situ STEM) with locally resolved nanoparticles, high spatial resolution, and chemical specificity. Additionally, changes in surface properties at different temperatures were tracked ex-situ by X-ray photoelectron spectroscopy (XPS), the crystal structure was investigated by X-ray diffraction analysis (XRD), size and morphology were characterized by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). The OER activities of synthesized iridium oxide nanoparticles were measured in half-cell measurements at forced convection. The stability was carefully studied by operando flow cell measurements that were coupled to online inductively coupled plasma mass spectrometry.[4] The iridium oxide catalyst calcined at the lowest temperature resulted in outstanding mass-specific activity outperforming the reference iridium oxide catalyst by a factor of 40. By gradual increase in calcination temperatures up to 800 °C, we observe improvement in the durability of the synthesized catalysts, being comparable to the reference catalyst, yet still with notable improvement in catalytic activity. This is the first report to synthesize iridium oxide nanoparticles at high temperatures with preserved size and morphology not exceeding 10 nm and allows for the determination of activity and durability of similarly sized nanostructures.[5] Literature:[1] M. Bernt et al. Chemie Ingenieur Technik 2020, 92, 31-39.[2] T. Reier, et al. ACS Catalysis 2012, 2, 1765-1772.[3] Y. Lee et al. The Journal of Physical Chemistry Letters 2012, 3, 399-404.[4] S. Geiger et al. Nature Catalysis 2018, 1, 508-515.[5] M.Malinovic et al. Advanced Energy Materials 2022, Manuscript submitted for publication.

Influence of Process Parameters on SOEC Performance

Solid oxide electrolysis cells (SOECs) are highlighted as futuristic Power-to-gas (P2G) devices that can provide reliable supply of hydrogen gas as a renewable energy carrier. Despite the great potential of SOECs there are many challenges facing their commercialization. In this work we investigated the influence of fuel electrode and process parameters on initial SOEC performance (500 hours). Electrolysis experiments were performed with both GDC (gadolinia doped ceria)-infiltrated and un-infiltrated Ni-YSZ fuel electrode under various hydrogen flow rates with different ratios of H2-H2O mix, and current density including open circuit conditions. All cells marginally improve in performance initially, then undergo a brief period of rapid decay followed by a stable performance. The observed three stages of variations in cell performance, in terms of length of time and rate of change, are dependent on the type of fuel electrode and experimental process parameters used. These are investigated employing I-V measurements, electrochemical impedance spectroscopy (EIS), distribution of relaxation time (DRT), and microstructural characterization. The role of GDC infiltration and process parameters driving these performance variations and efficiency of hydrogen generation is analyzed in this work.

Synergistic Microfluidic and Optical Performance Enhancements of Photoelectrodes for Space Applications

The realisation of long-term space missions as well as lunar habitats require reliable and efficient oxygen and chemical producing devices e.g., for life support, fuel generation and in-situ resource utilisation (ISRU). We have recently demonstrated that integrated semiconductor-electrocatalyst systems can be operated in microgravity environments generated for 9.2 s at the Bremen Drop Tower (Center of Applied Space Technology and Microgravity, ZARM) at terrestrial efficiencies, thus opening the possibility of utilising these photoelectrochemical (PEC) devices for chemical synthesis in space. 1,2 , 3 Our findings reveal that by altering the electrocatalyst surface morphology through nanostructuring, we can introduce catalytic hot-spots on the photoelectrode which - through their hydrophilic nature - can also enhance gas bubble detachment in microgravity and thus circumvent the near-absence of buoyancy.1,3 We have found that the surface hydrophilicity and electrocatalyst loading require however careful balancing as the most effective nanostructures for gas bubble desorption can also result in less catalyst material on the photoelectrode surface, which in turn leads to a non-optimal PEC device performance.Here, we present a combined theoretical and experimental microfluidic, optical and photoelectrocatalytic performance analysis of photoelectrodes with integrated, nanostructured electrocatalysts, aiming at providing a guideline for an optimal design for microgravity applications. Focusing on the hydrogen evolution reaction (HER) and a well-investigated photoabsorber for this reaction, p-type InP, we firstly built an optoelectronic model in COMSOL Multiphysics in pursuit of quantifying the optical performance enhancements of Rh and Pt electrocatalyst nanostructures such as nanopyramids, nanowires and sub-wavelength aperture holes.4 We then developed a microfluidic model using the same nanostructure geometries to predict the hydrophilicity of the device surface and subsequently, the gas bubble contact angle. The best-performing nanostructured photoelectrodes predicted in our models where then manufactured, photoelectrochemically tested and fully optically and spectroscopically characterised. Predicted local electric field enhancements through catalytic hotspot formation were moreover experimentally validated using scanning electrochemical cell microscopy (SECCM). Our findings indicate that our developed optoelectronic and microfluidic models can be utilised to design a theoretical framework for identifying ideal electrocatalyst nanostructures for microgravity applications.References Brinkert K, et al. Efficient solar hydrogen generation in microgravity environment. Nature Communications 9, (2018). Brinkert K, Mandin P. Fundamentals and future applications of electrochemical energy conversion in space. npj Microgravity 8, (2022). Akay Ö, et al. Releasing the Bubbles: Nanotopographical Electrocatalyst Design for Efficient Photoelectrochemical Hydrogen Production in Microgravity Environment. Advanced Science 9, 2105380 (2022). Tembhurne S, Haussener S. Integrated Photo-Electrochemical Solar Fuel Generators under Concentrated Irradiation. Journal of The Electrochemical Society 163, H988 (2016). Pan Y, Huang S, Li F, Zhao X, Wang W. Coexistence of superhydrophilicity and superoleophobicity: theory, experiments and applications in oil/water separation. Journal of Materials Chemistry A 6, 15057-15063 (2018).